Dry drilling of diamonds and the like



y 15511951v c. G. PETERS ET AL 5 2,552,582

DRY DRILLING 0F DIAMONDS AND THE LIKE Filed Dec. 23, 1946 P/FL-PAE/NG Fd/PM/NG fNLA/PG/NG FlLar COMPLETING BLANK Paar/lam l/auz fxrelvslon BELL FACE-5X DRYEECF- (owvEk- URYEECT- Cow GER- M/INUOW lF/C ORILL/IIG SINK/N6 klCflR/LLING lNK/NG 4070 60 MAN MINUTES Fig. 2.

B/eu TING Bear/Na Pzc KIN a I FLA T 5TAIPTING hoLs PR/mnmr (one 25 HOUR s INVENTORS CHA0NCEY 6. PETER s F0255? .HA R/S BY ATTORNEY Patented May 15, 1951 DRY DRILLING OF DIAMONDS AND THE LIKE Chauncey G. Peters, Calvert County, Md., and Forest K. Harris, Washington, D. 0., assignors to the United States of America as represented by the Secretary of Commerce Application December 23, 1946, Serial No. 718,093

7 Claims. (01. 125-30) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention herein described may be made and used by or for the Government of the United States without payment to use of any royalty therefor.

This invention relates to the drilling of diamonds and the like, and is particularly applicable in the production of wire drawing dies of such hard, crystalline material. The present invention is based on our discovery that diamonds and the like may be started and pilot drilled for the formation of the bell cones therein with greatly increased speed and with other marked advantages by impressing across a drill needle and stone condensed current and potential surges of short time duration applied to a non-rotated drill point in air or other gaseous environment with the energy of such surges controlled to maintain an energy input sufficient to produce disintegration at the point of contact by ionic bombardment but no so high as to cause a rise of temperature of the diamond that would initiate massive destruction thereof by oxidation. This discovery enables us to cause the rapid formation of a slender pilot hole or well in the diamond surface aligned with and entered by the needle point. The invention resides in the provision of a method of and apparatus for making practical application of this discovery in the drilling of diamonds.

The present invention is in part disclosed as a subcombination of the process of diamonddie production forming the subject matter of our copending joint application with Walter B. Emerson, Irving L. Cooter, and Karl F. Nefllen, now Patent No. 2,438,941, issued on April 6, 1948, wherein the present invention is employed for drilling the bell in the production of diamond dies. The present invention is likewise in part disclosed in the article published within one year prior to the present application in The American Minerologist 311156-160, and entitled Application of the High Voltage Are to the Cutting, Sawing, and Drilling of Diamonds, by Chauncey C. Peters, one of the present applicants.

As the invention is well exemplified by the application thereof to the drilling of the bell or primary cone of a diamond die of definite size, such application is herein described as illustrative but not restrictive of the invention.

(A) Die production in general In general, the production of diamond dies involves the following steps: (1) selection and preparation of die blanks, (2) spotting, or starting the hole, (3) drilling the bell or primary cone, (4)

V 2 drilling the secondary cone, (5) back-opening, and (6) polishing of the die surface. The present invention is particularly applicable to steps (2) and (3) of this procedure.

(B) Prior art practice (1) (2) In accordance with the prior art, for dies of .0015 inch diameter, or less, diamonds of /6 to carat, allowing a thickness of 1.3 to 1.8 millimeters, have been selected. The selected diamond has then been formed into a flat plate having two parallel surfaces spaced apart by the thickness of the die, this being generally accomplished by bruting. This blank has then been mounted and centered in a metal disc which is rotated in a bench lathe while asmall conical hole is spotted or bruted in one of the fiat surfaces of the stone with a diamond chip held in a pair of pliers, to act as a starting point for the drill. The blank is then ready for the drilling operation.

(3) The method and equipment developed in Europe for drilling diamond dies (see Paul Grodzinski, Diamond and Gem Stone Industrial Production, Chap. II, page 169) essentially employ a star-drilling action. The drilling machine has a horizontal, single spindle that rotates at about 3500 revolutions per minute and carries a sewing needle for the drill. The diamond is mounted on a second spindle which oscillates the diamond against the sharpened end of the drill. Diamond dust of different grades mixed with alcohol or oil is used as the abrasive. Domestic machines as heretofore employed have operated on the same principle but usually employ ten vertical spindles to conserve space and facilitate inspection by the operator.

For drilling the primary cone, in the prior art the spotted blank is placed on the rough drilling machine, using a needle of about .040 inch diameter ground to a rather blunt point. Diamond dust of about micron grade (our designation for dust having an average particle size of from 50 to microns) is used for the first part of the operation, and of about 30 micron grade (25 to 35 microns) for the finish. In this way the bell is formed, preferably as a 60 cone of about 1 millimeter or .040 inch depth.

The time required to complete the spotting of a die by the old bruting method usually amounts to about /2 hour, and the time for drilling the primary cone by the old method averagesfrom 10 hours to 25 hours.

(C) Objects of the invention The present invention in this embodiment has for objects severally. and interdependently the material. reduction ofthe time heretofore required for starting the hole in the diamond, the

provision of a new electrical dry drilling method.

for forming pilot wells in the diamond; and the provision of a new pilot drilling and-counters nk: ing method of forming bell cones. Further objects and advantages of the;invention,will beepparent from the detailed description of the illustrative embodiment of method and means incorporating its principles.

(D) The new procedure Briefly, in applying the present invention in the production of small diamond dies, following preparation of the blank by any suitable method, for example, that of the copending applicationabove mentioned; we spot drill a pilot hole in the diamond surface by our new dry drillingmethod, shape itito the form of a wide-angle, say 90, cone prcferably'by anew. countersinking method employing a blunt countersinking needle and, eliminating'th'e star d'rillingiprinciple, extend a second pilot hole from the bottom of the widegangle come. by; our newelectrical dry drilling method, and shape theresulting funnel+ shapedhole into a finalprimary cone which may bea 40 to 70 cone; for'example, preferably by the new countersinking method.

In the accompanying drawings of. embodiments illustrative-ofjthe several features of this invention:

Fig. 1- is a flow diagram-of the-steps offorming a primary cone in accordance with the in-- vention'.

Fig. 2 is a comparative diagram of the conventional prior art process.

Fig.- 3a is a diagram of the dry drilling method and means.

Eig. 3b-is a perspective view of oneembodiment of dry dr-illing'stand;

Fig. 4 is a diagramofcountersinking apparatuspartly in section.-

Referringto Figs; 1 and 2aof the accompanyingdrawings, Fig; l illustrates diagrammatically operations performed on the,-blank by" our new method, and Fig; 2 showsinsimilar-diagram for reference andcomparison the steps employed in the prior-art. In-these-figures, for ease of reference the several-procedural steps-.are numbered and described with legends-showing the approximate time to perform'them.

Asiindicated'inFig. 1, byour new" procedure after-the die blank, has been prepared, as bycutting and polishing. itsfacial. surfaces, a pilot hole is foredrilled into-the diamond-bymeans-rof anrelectric spark, and the .operation is=completed by, a light commercial. drilling machine modified to effect countersinking, Inthelatter. operation the rotating drill follows the.v pilot hole, without beingdeterred by apexial contact withthe diamond, and the conicalsurface of thedrill, which is rotated with considerable peripheral speed, actsas a countersink orreamer-forshaping the contours of'the cones and applying the polish to the cone and bearing surfaces. Thus the tedious and time consuming star drilling operation,- which is the basisof "prior methods, is eliminated, and the strains, flaws, andffractures, and other damage, to the bearing, surfaces, frequently resulting; from' preparingtheblank and spotting the die by bruting, is avoided;

(1) Preparing the blank In applying the present invention in the production of small diamond dies of the type disclosed in the above mentioned copending appli cation. as the first step the blank is preferably prepared with two polished parallel surfaces and a polished window face at right angles thereto. Anyvdesired'l method may be employed for preparing the blank, that disclosed in the above mentioned copending application being preferred.

For forming the bell, in accordance with the presentlinvention the blank prepared in any suitable manner by step. (1) is subjected to further steps as follows: (2) The blank is pilot drilled electrically; (3) The hole is then enlarged by mechanical countersinking; (4) The pilot hole is then extended; and The bell shape may then be completed by mechanical countersinking, all as illustrated diagrammatically in Fig. 1. As there indicated, this complete operation by the present invention may be performed in from -to minutes as-compared withlO to 25 hours by the old bruting and pecking method (Fig. 2, diagramsZand 3). Eachof these steps will now be-considered in detail.

(2) Foredrz'lling the pilot hole For forming the pilot hole or well, step (2) Fig. 1, apparatusis preferably used-corresponding to thatillustratedin Figs. 3a and 3b. As shown in Fig; 3a. the leads from the volt, 60 cycle A. C. outlet are connected to the primary terminals of a-.731"0.t0' volt output. adjustable ratio autotransformer such as a variac V and the secondary of the variac is connected to the: primary of a power-transformer T which may bear 5000 volt, 300volt-ampere power transformer or a 20 milliampere'neon-sign lighting transformer'as above described. When employing the 5000 volt, 300 watt power transformer a resistance R which may. have avalue of about'70'ohms is placed in the-primary lead of the transformer and an A. C. ammeter A of approximately'two amperes range in the other. A capacitor C of about .001 to .008 microfarad is connected across the secondary leads of the-transformer. This produces across the diamond acondensed spark'discharge of very short duration and thus limits heating of the diamond. The rheostat R. can'be'dispensed withif a current limiting transformer such as a'12,000 volt, 20 milliampere neon sign lighting transformer is'used instead of the power transformer;

Control and speed of drilling is improved by insertinga quenched spark gap G in the secondary-lead between the transformer T and the capacitor C. This prevents the'formation of a power are follow-up in the circuit that would overheat and'spoi-l the diamond. When this is done, however, the apparatus'must be enclosed ina metallic shield S-to avoid radio-interference.

As shown in Fig; 3b, the drill stand for dry drilling of the pilot hole provides'a metallic support forthe diamond and an aligning support for the drilling. needle together with electrical connections 8; 9, for connecting these two elements across thecondenser C, Fig. 3a. In the simple form of stand shown in Fig; 31) for purposes of illustration, two 3-inch brass angle pieces I0, [I are fastened to a wooden pillar 12 which is-supported-by thebase-IS; A small brass rod l0 weighing approximately Ste 10 grams, slidesclosely but with minimum'friction through two aligned guide holes drilled in thebrass angle pieces. Into the lower end of the rod I4 is fastened the drilling needle l5 which for the purpose of step (2) in Fig. 1 is preferably a 70% platinum, 30% iridium wire approximately .020 inch in diameter. A brass block I6 provided with an upstanding brass table I! supports the diamond die blank I8.

With the arrangement shown in Figs. 3a and 3b it is not necessary to secure the unmounted diamond D to the pedestal I! at all, but if desired, we contemplate effecting such securement in any suitable way, for example, by the use of a drop of cellulose acetate cement, such as that currently sold under the trade-name Duco cement, between the diamond and the top of the pedestal H to prevent shifting of the diamond relative to the electrode I8, particularly during the initial spotting operation.

In this operation the end of the drill needle 15 is ground to a cone of about 20 degrees, and

the point is brought into contact with the center of the flat surface of the die blank [8. The current is then applied and adjusted by means of the variac V until a white spark extends from the needle !5 to the brass pillar [1. This should occur when the ammeter A reads about 1 ampere. The drilling proceeds rapidly with the diamond supported in the air or other gaseous atmosphere, and is a dry drilling procedure effected without wetting of the stone or immersion of it in any electrolyte. If the end of the drill I5 becomes red the current should be reduced by adjusting the variac V until the color.

disappears. The current should, however, be sufiicient to maintain the white spark between the drill l5 and the pillar H. In about 20 minutes time a roughly cylindrical hole, Fig. 1, step (2), about 0.5 mm. (0.020 inch) deep and .2 mm. (0.008 inch) in diameter, is drilled in the diamond and the end of the drill I5 is disintegrated. Very little progress is made at this point by repeating the dry drilling operation with a resharpened needle.

(3) Countersinking According to our invention, therefore, the foredrilled blank I 8 is next mounted on the light drilling machine employing a suitable blunt or wide-angled countersink, for example, a No. 1 drill needle, sharpened to a 90 cone and rotated at a relatively high speed, for example, 3200 R. P. M. Using grade 45 micron powder in alcohol or any other suitable vehicle, and reciprocating the diamond axially of the needle at a slow rate, say 200 times per minute, sothat the powder may enter between the needle point and diamond surface, the bell cone is then countersunk to the bottom of the foredrilling as indicated in Fig. 1, step (3), in about 45 minutes. During this operation the die is applied against the countersinking point about of the time with a very light pressure, of the order of a few grams, and the distance of reciprocation of the diamond away from the needle point may be of the order of a half millimeter.

Suitable apparatus for the performance of this step is diagrammatically illustrated in Fig. 4 in which the drill needle 20 is carried by a vertical shaft 2| rotated in a bearing 22 by any suitable means as the cord and pulley drive 23. The diamend I8 is mounted on a support 24, which is shown as provided with a height adjusting means 25, and carried by an arm 26 pivoted at 2 l and adapted to raise and lower the support 24 as aforesaid. In the form shown a lightly loaded counterweight 28 lifts the diamond against the drillpoint, and the arm reciprocating cam 29, suitably driven, effects the displacement of the blank [3 from contact with the drill point.

For convenience in the machine drilling, the blank 18 is mounted in a newly developed small window-nib illustrated in Fig. 4. This nib, in the form shown, comprises a cylindrical cupshaped member 30 provided with two diametrically aligned viewing openings 3| and with a close fitting cylindrical plug 32 having a conical reser oir 33 to hold the dust-and-vehicle mixture. The reservoir 33, as shown, narrows to an axial center opening, and the diamond blank is sealed to the plug 32 by a thin layer of wax on the bottom of the plug in the space 34 surrounding this center opening. This layer of wax prevents leakage of the cutting mix and also enables the blank [8 to be lifted from the cup 30 by lifting out the plug 32, which may be provided with a flange around its upper end to facilitate its removal, if desired. Beeswax, dental wax, or the like, makes a good seal from which the diamond is easily disengaged. The window on the diamond, when it is secured in the nib, is aligned with the openings 3!, so that the progress of the drilling may be seen through one of these openings, the blank being illuminated by light shining through the other. With this unit the blank l8 can be mounted or unmounted in a few moments.

(4) Pilot extension In the next step, Fig. 1, step (4) by repeating the dry drilling operation of step (2) (see Figs.

(5) Finishing the bell Following the pilot extension the blank is again returned to the drilling machine, and further countersunk with a needle ground to a cone, as shown in Fig. 1, step (5). Using grade 20 micron powder at the start and grade 6 micron powder to finish, a smooth 60 cone about 1.0

mm. (.040 inch) deep is obtained in about an 7 hour. The set-up is generally like that employed in step (3) (see Fig. 4). At this point about 0.2 mm. (.008 inch) of the blank thickness should be left for the secondary cone. If the finished blank is to be more than 1.2 mm. thick, say 1.6 mm., further foredrilling and countersinking of the bell may be practiced.

(6) Further treatment After formation of the bell in accordance with the present invention, the secondary cone of the die may be formed in any suitable manner, and the die may then be completed by back-opening and blending and polishing as desired. Preferably these operations are performed in accordance with the method disclosed in the above mentioned copending application, but such further procedure forms no part of the present invention.

('7) Economies In forming a bell cone employing the present invention, the foredrilling and countersinking,

repeated until the desired depth of bell is obtained, may be efiected in about 3 hours per die. One operator can care for two electric drills or ten countersirrking spindles, and thus the time required for forming a bell by the present invention becomes approximately 40 to 60 man minutes per die.

By contrast, in the prior art bruting and pecking method an average of 2.5 man hours is required per bell, and inaddition considerable consumption of diamond chips and powder is inwolved in the bruting and pecking operations.

Thus the present invention effects a noteworthy saving of material, labor, and time, aside from producing a better and more uniform bell which in its initial production is generated with a well polished surface. These and other advantages may be more fully appreciated from a consideration of the aforesaid copending application and publication, to which reference is made in this connection.

From the foregoing description of a preferred method and apparatus illustrative of the invention, it will be appreciated that the invention is not limited to the precise embodiment disclosed, but includes modifications thereof, as will be apparent from the appended claims. Reference is also made to the aforesaid publication which discloses a further embodiment of the present invention exemplifying some of the modifications which may be made without departing from the broader aspects of the invention.

"Thus, in lieu of the sliding mounting of the needle I l-l5 in brackets ill-H (Fig. 3b) the needle-holder l4 may be suspended from a light coil spring, and this assemblage may be lowered to rest the tip of the needle l5 against the diamond with a suitable pressure. While pressures up to 10 grams may be employed, a pressure of about 0.5 gram gives extremely good results.

The needle l5 may have diameters other than 0.020 inch, but this particular diameter is especially eflicacious. During the drilling operation best results are obtained with the primary current adjusted to a value which is just below that causing a needle of 0.020 inch diameter to rise to a visible red heat. The limiting condition for rapid drilling seems to be the power that can be applied before frosting of the diamond occurs. Frosting never results when the exposed 0.020 inch diameter electrode is operated below its reddening temperature. With a 0.032 inch diameter electrode frosting occurs without visible reddening. Therefore, the 0.020 inch electrode enables the selection of the best power value for efficient drilling. With such electrode the variac V is adjusted until the 0.020 needle begins to present invention and is disclosed in the U. S.

patent to Kurtz et al. No. 2,377,159, which effects the perforation of the thin web so quickly that the heating problem is not there encountered. The heating problem here referred to is incident to the prolonged drilling of pilot wells by ionic "bombardment. In practicing the present invention the tendency to overheat when the drilling approaches the bottom of the diamond may be overcome by mounting the diamond being drilled upon another fiat surfaced diamond silver soldered in a cavity in the block [6 and protruding about0.5 mm. above the metal surface. The pedestal i1 is dispensed with in this arrangement.

In the practice of this invention, the electrode preferably is tapered to a tip diameter of from 0.002 to 0.003 inch, and the electrode is preferablygiven an occasional rotation of a fraction of a turn. This procedure tends to result in the uniform production of a well-shaped symmetrical hole. In the dry drilling of the pilot holes, it is also desirable to drill for about ten minutes and then continue the drilling with a re-sharpened electrode for another ten minutes, in lieu of continuously employing the same electrode for a 20 minute drilling period. It is also desirable to employ protective glasses while observing the condition of the spark during the drilling operation, to avoid injury to the operators eyes.

What is claimed is:

'1. A method of dry drilling pilot wells in diamonds and like hard, crystalline stones which comprises supporting the diamond in a gaseous atmosphere on an electrically conductive base, pressing lengthwise against the diamond an electrically conductive needle point, creating a condensed electrical spark discharge around said diamond between said needle point and base, controlling the power input of said condensed spark discharge to cause disintegration of the diamond at the needle contact area by ionic bombardment without heating the diamond to a tempera ure causing massive destruction thereof by oxidation, and continuing such controlled condensed spark discharge for a time sufficient to produce a Well in the diamond aligned with and entered by said needle point.

2. A method of dry drilling pilot wells in diamonds and like hard, crystalline stones which comprises supportin the diamond in a gaseous atmosphere on an electrically conductive base, pressing endwise upon. the dia1nondwith a pressure of about 0.5 to 10 grams-the tip of a platinum-iridium wire having a diameter of about 0.02 inch, creating a condensed electrical spark discharge around said diamond between said wire and said base, controlling the power input of said condensed spark discharge to cause disintegration of the diamond on the needle contact area by ionic bombardment without heating the diamondto a temperature causing massive destruction thereof by oxidation and continuing said discharge until a well has been formed in the diamond having a depth of about 0.02 inch and a width at its top of about 0.008 inch.

3. A method of dry drilling diamonds and like hard, crystalline stones which comprises elec-- trically foredrilling a pilot well in the diamond by the method of claim and thereafter countersinking said well with a rotating blunt needle point and diamond dust to a depth approaching the depth of said pilot well.

4. A method of dry drilling diamonds and like hard, crystalline stones which comprises electrically foredrilling a pilot Well in the diamond by the method of claim 1, then countersinking said well with a rotating blunt needle point and diamond dust to a depth approaching the depth of said pilot well, and then drilling by the method of claim 1 a further well extending from the bottom of the countersunk well.

5. A method of dry drilling diamonds and like hard. crystalline stones which comprises elecrically foredrilling a pilot well in the diamond by the method of claim 1, then countersinking said well with a rotating blunt needle point and diamond dust to a depth approaching the depth of said pilot well, then f-oredrilling a second pilot well from the bottom of the countersunk well by 9 the method of claim 1, and thereafter further countersinking the well to a depth approaching the total depth of the second well.

6. Apparatus for dry drilling pilot Wells in diamonds and like hard, crystalline stones comprising an electrically conductive base for supporting the diamond, a needle-like drill point, means for pressing said drill point endwise towards said base, and against a diamond supported thereon, a condensed spark discharge circuit connected across said needle and base, said discharge cir cuit comprising the secondary of a high voltage transformer, a quenched spark gap and a capacitor connected to be charged from the transformer secondary through the gap, said capacitor being connected in parallel with the path between said drill point and base, and means for adjusting the power in said condensed spark discharge circuit to a value sufiiciently high to create a spark discharge around the diamond embraced between said needle and base and efiect disintegration of the diamond at the needle contact area by ionic bombardment but not so high as to heat the diamond to a temperature producing massive destruction of the diamond by oxidation, so as to produce a Well in the diamond aligned with and entered by said needle point.

7. Apparatus according to claim 6, said drill point being formed of platinum-iridium Wire having a diameter of about 0.02 inch.

CHAUNCEY G. PETERS. FOREST K. HARRIS,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 971,935 Simon Oct. 4, 1910 1,922,497 Peterson Aug. 15, 1933 2,258,480 Bergmann et al Oct. 7, 1941 2,300,855 Allen et al Nov. 3, 1942 2,377,159 Kurtz et a1 May 29, 1945 2,398,250 Robbins Apr. 9, 1946 2,452,141 Pasdertz Oct. 26, 1948 

